A lithium-ion secondary battery has begun to be used in electric transportation means (for example, electric vehicles) for providing power under its high energy, high capacity and high power. Electrochemical performance of the lithium-ion secondary battery is improved, while safety of the lithium-ion secondary battery as a power source in the electric vehicles must be strictly ensured. The lithium-ion secondary battery should pass abuse test under harsh conditions for meeting requirements on safety performance in practical use, and three extreme safety tests including nail penetration, crush test and overcharge are generally performed.
In the crush test of the lithium-ion secondary battery, a positive electrode plate and a negative electrode plate contact with each other directly or through a non-insulative medium at local regions inside the lithium-ion secondary battery, an internal short-circuit occurs in the lithium-ion secondary battery. As many short-circuit points and large short-circuit current are generated in the crushing, decomposition and gas production of the electrolyte and internal overheating in the lithium-ion secondary battery will be caused, which may cause fire and explosion of the lithium-ion secondary battery.
In order to solve the above problems, a design idea in the prior art is to allow an external short-circuit to occur in the lithium-ion secondary battery before the internal short circuit occurs in the lithium-ion secondary battery, the large current generated from external short-circuit rapidly releases internal energy of a cell of the lithium-ion secondary battery, so as to ensure that the lithium-ion secondary battery has not energy enough to cause fire and explosion after the internal short-circuit.
A rechargeable safe battery capable of improving anti- puncturing and anti-crushing performance is disclosed in Chinese patent application publication No. CN102088113A, published on Jun. 8, 2011 in which two conductive support plates are disposed between a case and an electrode assembly. Under a normal condition, the two support plates are respectively electrically connected to a positive electrode and a negative electrode of the lithium-ion secondary battery, and are insulated from the case; when the lithium-ion secondary battery is punctured or crushed, the two conductive support plates establish an electrical connection, namely a short-circuit is realized between the positive electrode and the negative electrode of the lithium-ion secondary battery. As the conductive support plate is made from a conductive metal having a very low resistance, when the conductive support plates are short-circuiting, a large current is generated. Therefore heat generated by the large current is rapidly released to outside, so as to avoid that the heat generated by the large current when the lithium-ion secondary battery is internal short-circuiting is accumulated in the lithium-ion secondary battery, and so as to effectively eliminate potential hazard.
The above design has many deficiencies in practical use, especially in the practical crushing process, as an insulative layer (generally is an insulative film) between the two conductive plates has a certain toughness, it can not be ensured that the electrical connection between the two conductive support plates is realized before the internal short-circuit caused by crushing.